3.2 Data processing
The data processing started with the adjustment of the
photogrammetric control points net, carried out by the StarNet
software. The accuracy associated at the distance measurements
has been assumed equal to 1 cm, being the control points only
natural points. The adjusted coordinates obtained are
characterized by an associate root mean square in the order of 1
mm. The calibration of the non-metric digital camera was performed
as well, in order to find the inner orientation parameters
together with full lens distortion; for this purpose was used the
PhotoModeler v5.0 self-calibration module, that perform the
bundle adjustment analytical model by using several images of
a plane test-field, supplied with the software. Of course, photos
must be taken with the same focusing condition of the
application case and, due to the planarity of the test-field, by a
convergent scheme of acquisition (figure 3); moreover, to
successfully recover the principal point position, it is
recommended to take some photos with the camera rolled
through 90° (Bitelli et al., 2003).